a. Field of the Invention
The present invention relates to a plug and more particularly, to a swivel plug.
b. Description of the Related Art
A conventional electric plug 1, as shown in FIG. 1, has the metal conducting blades 11 axially extended from the front side of the housing 12. This design of electric plug 1 requires much vertical installation place. FIG. 2 illustrates another structure of electric plug that requires less vertical installation space. As illustrated, the electric plug 2 comprises a housing 22, two metal conducting blades 21 perpendicularly extended out of the bottom side of the housing 22, a pull ring 24 coupled to the housing 22 for pulling by hand to remove the metal conducting blades 21 from the electric socket. U.S. Pat. No. 5,567,181 discloses a similar design. This design of electric plug provides handle means to facilitate grasping. However, pulling the pull ring or handle means causes a concentration of stress. Because the housing is slightly softened when the internal circuit is bearing a load to produce heat, pulling the pull ring or handle means may cause damage to the housing. Is this design is employed to an electric plug having two metal conducting blades and one grounding prong, pulling the pull ring or handle means may bias the housing, thereby increasing pulling resistance, and much effort should be employed to remove the electric plug from the electric socket. Further, this design of electrical plug still requires much horizontal installation space.
FIGS. 3–4 show a three prong swivel plug constructed according to U.S. Pat. No. 5,658,152. According to this design, the contacts 32 of the front female plug portion and the contacts 31 of the rear male plug portion each have a laterally extending protrusion 321 or 311. The laterally extending protrusions 321 of the front female plug portion are respectively coupled to the laterally extending protrusions 311 of the contacts 31 of the rear male plug portion. This contact connection arrangement greatly reduces the height of the housing of the swivel plug. However, the contact side is unstable, not suitable for transmitting a big current. When transmitting a big current, a high temperature will be produced due to unstable contact between the contacts.
U.S. Pat. No. 6,663,396, issued to the present inventor, disclosed an electric plug having horizontal/vertical installation modes. According to this design, as shown in FIGS. 6 and 7, rivets 511, 512 are used to pivotally connect the conducting blades 41, 42 to the metal terminals 51, 52, for enabling the front housing 4 to be turned relative to the rear housing 5 about an axis X—X between two positions within 90 degrees. Referring to FIGS. 7C and 7D, when a grounding prong 43 and a grounding terminal 53 are added to the electric plug, the distance D between the two adjacent pivots 511, 531 is too short to meet the related safety code. FIGS. 8A and 8B show the rivet 511 fastened to the conducting blade 41 and the respective metal terminal 51. Because there is a limitation to the height H of the conducting blade 41 and the metal terminal 51 (normally limited to about 5–6 mm), the size of the heads and shaft of the rivet 511 must be relatively constrained, i.e., the heads and the shaft of the rivets 511 must not surpass 5 mm and 2 mm respectively. However, a relatively bigger rivet provides a relatively greater contact area and a relatively stronger retaining force. According to the embodiment shown in FIG. 8B, the rivet 511 provides a strong retaining force to join the conducting blade 41 and the metal terminal 51. However, it requires much effort to turn the conducting blade 41 relative to the metal terminal 51. According to the embodiment shown in FIG. 8C, a spring washer 512 is mounted on the rivet 511 and stopped between one head of the rivet 511 and the metal terminal 51. The use of the spring washer 512 prevents locking of the conducting blade 41 to the metal terminal 51, however it relatively increases the assembly time and cost. Further, because the heads of the rivet 511 respectively protruding over the conducting blade 41 and the metal terminal 51, thereby increasing the combined thickness T1 or T2.
Therefore, it is desirable to provide a swivel plug that eliminates the drawbacks of the aforesaid prior art designs.